Gas turbine engines emit various pollutants including oxides of nitrogen ("NOx"). NOx is primarily formed through the thermal fixation of nitrogen and results from the high temperature combustion of fuel and air in the gas turbine engine. Environmental concerns and more stringent governmental regulation of NOx emissions have prompted designers to investigate various methods for reducing the generation of NOx by gas turbine engines. Examples of devices for reducing or controlling NOx are disclosed in the following commonly assigned patents: (1) Snyder et al., U.S. Pat. No. 5,256,352 issued Oct. 26, 1993 entitled Air-Liquid Mixer; (2) McVey et al., U.S. Pat. No. 5,263,325 issued Nov. 23, 1993 entitled Low Nox Combustion; and (3) Marshall, U.S. Pat. No. 5,406,799 issued Apr. 18, 1995 entitled Combustion Chamber.
Two basic approaches for a low NOx fuel injection system are (1) a locally lean stoichiometry system and (2) a locally rich stoichiometry system. It is desirable in a fuel rich approach to operate in the fuel spray equivalence ratio above 1.6 prior to rapidly quenching down to appropriate lean burning levels. The rich based system also requires a rapid mixing process controlled at some distance downstream of the fuel injection apparatus so that excessive Nox is not produced during the quenching process. However, the rich approach is susceptible to a potential increase in smoke. It is therefor desirable to provide a fuel-rich combustor system and method of operation which reduces Nox without a detrimental increase in smoke.